1. Field of the Invention
The present invention relates to an apparatus for driving a piezoelectric element which is used as a fuel injection valve of a gasoline engine, a diesel engine, or the like.
2. Description of the Related Art
A high response characteristic piezoelectric element is applicable to an actuator of a fuel injection apparatus of a gasoline engine, a diesel engine, and the like (see: Unexamined Japanese Patent Publication (Kokai) Nos. 60-249877 and 62-17338). For example, there is suggested a fuel injection apparatus which includes a plunger driven by an engine; a fuel pressure chamber filled with fuel and pressurized by the plunger; a needle move in response to a fuel pressure within the fuel pressure chamber, the needle being opened when the fuel pressure is larger than a predetermined pressure; an overflow valve associated with a valve member which is slidably inserted into a slidable hole and is controlled by the pressure within a pressure control chamber arranged coaxially with the slidable hole; and a variable volume chamber connected to the pressure control chamber and changed by an actuator, to thereby close the overflow valve to shut off the fuel from the fuel pressure chamber when the volume of the variable volume chamber is reduced, to increase the pressure within the pressure control chamber.
In the above-mentioned fuel injection apparatus, however, to initiate a fuel injection, when the volume of the variable volume chamber is reduced to increase the pressure within the pressure control chamber, the overflow valve associated with the valve member is moved at a high speed, and thereafter, the overflow valve is rapidly moved on to a valve seat. As a result, although the overflow valve and the valve member are closed at the same time, the overflow valve and the valve member bounce and thus do not remain on their valve seats, whereby the overflow valve is again opened. Therefore, since an overflow of the fuel in the fuel pressure chamber occurs, the fuel injection pressure can not smoothly rise to a high pressure.